1. Field of the Invention
The present invention generally relates to local oscillator circuitry, and more specifically to providing a local oscillator signal using digital circuitry.
2. Background Art
Television signals are transmitted at radio frequencies (RF) using terrestrial, cable, or satellite transmission schemes. Terrestrial and cable TV signals are typically transmitted at frequencies of approximately 57 to 860 MHZ, with 6 MHZ channel spacing in the United States and 8 MHz channel spacing in Europe. Satellite TV signals are typically transmitted at frequencies of approximately 980 to 2180 MHz.
Regardless of the transmission scheme, a tuner is utilized to select and down-convert a desired channel from the TV signal to an intermediate frequency (IF) signal or a baseband signal, which is suitable for processing and display on a TV or computer screen. The tuner should provide sufficient image rejection and channel selection during down-conversion as is necessary for the specific application. The National Television Standards Committee (NTSC) sets standards for television signal transmission, reception, and display. To process a NTSC signal, it is preferable that the tuner have a high-level of image rejection. However, less image rejection is acceptable for non-NTSC signals depending on the specific application and the corresponding display requirements.
A downconverter generally mixes a local oscillator signal and the RF input signal to provide the downconverted signal. The circuitry used to generate the local oscillator signal often includes large inductors and/or capacitors, which can increase the size and cost of the circuitry.
What is needed is a method or apparatus for providing the local oscillator signal using digital circuitry.